Process for fracturing and propping an unconsolidated subterranean formation



y 2, 1957 J. HUITT ETAL 3,316,967

PROCESS FOR ["RACTHRING AND PRUFllNG AN UNCONSOLIUATED SUBTERRANEAN FURMATION Filed Sept. 30, 1964 United States Patent 0 PROCESS FOR FRACTURING AND PROPPING AN UNCONSOLIDATED SUBTERRANEAN FORMA- TION Jimmie L. Huitt, Glenshaw, and John Papaila, Apollo,

Pa., assignors to Gulf Research 85 Development Company, Pittsburgh, Pa., a corporation of Delaware Filed Sept. 30, 1964, Ser. No. 400,526 17 Claims. (Cl. 166-42) This invention relates to a method for completing a well bore penetrating an unconsolidated subterranean rock formation. In particular, this invention describes a method for propping a fracture created in an unconsolidated formation.

Many underground rock formations are unconsolidated or so poorly consolidated that they disintegrate under the forces exerted upon them by the weight of the overbearing rock and by the flow of formation fluids into a well bore penetrating the formation. Such rock formations are hereinafter referred to generally as unconsolidated formations.

Various methods have been suggested for producing fluids through a well bore penetrating an unconsolidated formation while preventing the entry into the well bore of individual formation particles. In one such method, a slotted or otherwise perforated pipe or liner is centralized in the well bore and the annulus around the liner is packed with gravel. However, placement of the gravel pack in the well bore is a cumbersome, expensive and time consuming operation that greatly reduces the diameter of the well bore extending through the unconsolidated for mation. Furthermore the gravel pack is used to filter the formation particles from the produced fluids and prevent their entry into the liner. Generally the accumulation of formation particles in the interstices of the gravel pack eventually results in plugging of the gravel pack around the well bore.

It has been suggested also that a well bore penetrating an unconsolidated formation can be completed by setting a perforated casing through the unconsolidated formation and placing an aggregate of graded gravel in the well bore and formation behind the casing at the perforations to prevent the flow of formation particles into the casing. That well completion method does not employ a screen to keep the gravel in place, but rather employs the larger gravel particles to bridge the casing perforations and prevent movement of the gravel into the well bore. In some instances the bridging action is not accomplished at all and in other instances, although the gravel initially bridges the casing perforations, it is later disrupted by the flow of fluids, especially formation water, through the perforations thereby permitting the entry of gravel and formation particles into the well bore or plugging the gravel pack around the perforated casing.

It has been suggested further that a well bore penetrating an unconsolidated formation can be successfully completed by creating a fracture in the formation around a cased well bore and propping the fracture with an aggregate of granular solids normally referred to as propping agents. However such fracturing methods are usually unsuccessful because the individual formation particles flow through the interstices between the propping agents, thereby plugging the well bore and the fracture.

It is an object of this invention to provide a method for completing a well bore penetrating an unconsolidated formation whereby the fluid flow capacity of the formation is increased and the entry of formation particles into the fracture and the well bore is prevented.

This invention resides in a method for propping a fracture around a cased well bore in an unconsolidated rock 3,316,967 Patented May 2, 1967 formation by injecting down the well bore and into the fracture a first liquid containing lamellar solid particles adapted to prevent movement of the formation particles into the fracture and displacing the first liquid with a second liquid containing a propping agent comprising granular solid particles that are displaced into the fracture to prop the fracture faces apart and sustain the lamellar particles in contact with the fracture faces.

An embodiment of this invention is described herein with reference to the accompanying drawings in which FIGURES 1 through 3 are views, in vertical cross section, of a Well bore penetrating an unconsolidated formation during various stages of the process of this invention.

FIGURE 1 is a view of the fractured formation during the covering of the fracture with a lamellar supporting agent.

FIGURE 2 is a view of the fractured formation during the placement of the granular propping agent in the fracture.

FIGURE 3 is a view of the fractured and propped formation during the production of formation fluids through the layers of lamellar supporting agents and the aggregate of propping particles in the fracture to the well bore.

According to the method of this invention, a fracture in an unconsolidated formation is completed by first depositing on the fracture faces a substantially complete covering of lamellar particles adapted to prevent the entry of individual formation particles into the fracture. Thereafter, the lamellar particles are maintained in position, and the fracture is propped open, by the deposition in the fracture of an aggregate of granular solid propping particles. As used hereinafter, the term supporting agent" refers to any lamellar or plate-like, solid or plastic particle that resists corrosion or solution in the injected and formation fluids and that has physical dimensions adapted to bridge at least two formation particles and to permit passage of the supporting particles, in a suitable transporting liquid, through the pumping and well bore apparatus and into the fracture. The supporting particles may be permeable or impermeable, as explained more fully below, and are preferably fibrous or membranous. Suitable supporting agents for the process of this invention can be strips, sheets, flakes, shavings, strands and other analogous forms consisting of such materials as polyvinyl chloride, polyvinyl acetate, cellulose acetate, cellulose nitrate, melamine formaldehyde, phenol formaldehyde and urea formaldehyde. This process can be effectively employed with such supporting materials as cloth particles, plastic sheet particles, leather and paper. Particularly effective as a supporting agent is plastic sheeting made of the particular compounds of polystyrene, polyvinyl or analogous materials that are insoluble in crude oil.

The dimensions of the individual supporting particles are adapted to permit transport of the particles through the pumps and fluid conduits of the well apparatus and to permit the placement of the supporting particles on the fracture faces to prevent movement of formation particles into the fracture without bridging or plugging of the supporting particles in the fracture. It is preferable that the individual supporting particles have a substantially square or rectangular shape to assure the bridging of the spaces between individual propping particles and individual formation particles. Also, the supporting particles should be larger than the formation particles to prevent movement of the formation particles, and it is preferred that the supporting particles have a largest dimension greater than twice the largest dimension of the individual propping particles to assure that each of the supporting particles are sustained in contact with the fracture face by at least one propping particle. The supporting agent is suitable for use with the process of this invention if each individual supporting particle has a length of from about ,5 to about 1.0 inch and a width of from about A to about 1.0 inch. To assure effective placement of the supporting agent in the fracture and substantially complete coverage of the fracture faces by the supporting particles, it is preferred that the individual supporting particles have a length of about A; to about inch and a width of from about to about inch. The maximum allowable thickness of the individual supporting particles is determined by the anticipated fracture Width and it is desirable that the thickness of the supporting particle be equal to about ,4 the width of the fracture. Preferably, the supporting particle should have a thickness of 0.005 inch, or less.

The transporting liquid for the supporting agent is hereinafter referred to as the spearhead liquid and is preferably a low fluid loss liquid having sufficient viscosity to support the transporting agent in its passage through the pumps and other well apparatus downwardly through the well bore and into the fracture without excessive deposition of the supporting agent in the well bore or bridging of the supporting agent across the entry of the fracture. As used in this application, low fluid loss liquid" is defined as a liquid which, with respect to the natural well bore fluids such as water or crude oil, has less tendency to filter through the formation. The low fluid loss property of the spearhead liquid is instrumental in creating or extending the fracture and in displacing the individual supporting particles into contact with the fracture faces. It is therefore desirable that the spearhead liquid have a filter loss of less than 200 cc. in a 25 minute test performed according to the standard test conditions prescribed in Recommended Practice, Standard Procedure for the Evaluation of Hydraulic Fracturing Fluids," American Petroleum Institute, RP 39, July 1960. It is preferred, however that the spearhead liquid have a filter loss ranging from about 10 cc. to about 50 cc. to assure effective placement of the supporting agent on the fracture faces.

The viscosity of the spearhead liquid must be adjusted to assure that the liquid will sustain the individual supporting particles in suspension as the mixture of supporting agent and spearhead liquid is displaced into the fracture. The spearhead liquid may comprise either an aqueous or hydrocarbon liquid or gel that contains various bodying agents to adjust the viscosity. Bodying materials are those such as colloid materials, a metallic salt of an organic acid, a high molecular weight olefin polymer, and a molecular linear polymer such as polypropyl ene. Specific examples of spearhead liquids that are suitable for the process of this invention are water containing guar gum and oil mixed with fatty acids and caustic compounds which react to form a gel in the formation. The spearhead liquid should have a viscosity of from about 10 centipoises to about 5000 centipoises or higher. A viscosity of from about 30 to about 100 centipoises is preferred for the spearhead liquid because such liquids provide an adequate transporting medium for the supporting agent and yet pass relatively easily through the pumps and other well apparatus.

The concentration of supporting agent in the spearhead liquid depends on the total quantity of supporting agent required. Effective support of the fracture faces and the prevention of entry of the formation particles into the fracture requires that the fracture faces be substantially covered by the supporting particles. Because of the difficulty in obtaining a uniform monolayer of the supporting particles to cover the fracture faces completely. it is more practical to supply sufficient supporting agent to form a multilayer of supporting particles over the fracture faces. Therefore it is desirable that the total surface area of the supporting particles available for contact with the fracture faces be equal to at least twice the area of the fracture faces themselves. To assure substantially complete coverage of the fracture faces throughout the lateral extent of the fracture, it is preferred that the total surface area of the supporting particles available for contact with the fracture faces be equal to an area of from about four to about ten times the area of the fracture faces. In this context the phrase, area of the supporting particles available for contact with the fracture faces, is employed to indicate that, since only one side of each supporting particles is in contact with the fracture face during the process of this invention, the effective surface area of the supporting agent is equal to one half of the total surface area of all the supporting particles contained in the spearhead liquid. When the required quantity of supporting agent is ascertained, the concentration of supporting particles per unit volume of spearhead liquid is determined by the anticipated volume of fluid loss and the limitations on pumpability and handling of the mixture of: spearhead liquid and supporting agent. A generally suitable spearhead liquid is one having a concentration less than 80,000 supporting particles per gallon of spearhead liquid, although in a particular instance a. greater concentration might be practicable.

As was indicated above, the individual supporting particles may be permeable or impermeable. In either case, during placement of the supporting particles, they are maintained in contact with the fracture faces under the force exerted by the spearhead liquid injected into the fracture. Subsequently they are supported by the individual propping particles in the fracture. After the fracture is supported and propped and the pressure on the liquids in the well bore is reduced, fluids flow from the unconsolidated formation through the fracture faces. Although the flow rate per unit area of the fracture face is small, the total volume of formation fluids flowing through the fracture is large and generally economically significant because the areal extent of the fracture is large. Where permeable supporting particles are employed, the formation fluids flow through the supporting particles themselves, and through the interstices between the supporting particles, into the pores between the propping particles and through the fracture into the well bore. Where impermeable supporting particles are employed, the fluids flowing from the formation pass only through the interstices around the individual supporting agents and then through the propping aggregate. Therefore the use of permeable supporting particles is preferred where higher rates of fluid flow from the formation are required.

An impermeable suporting agent has the advantage of forming an impervious cake on the fracture faces during the placement of the agent, thereby reducing the fluid loss of the spearhead liquid. However it is sometimes also desirable to employ a permeable supporting agent during the production of formation fluids in order to assure a higher rate of production from the fracture. In such instances it is possible to employ permeable supporting particles, the surfaces of which have been coated with an impermeable material that is soluble in the formation fluids. With such a coated supporting agent the individual particles are impermeable during their placement and therefore effectively seal the fracture faces and reduce fluid loss. Thereafter when the supporting particles are contacted by the formation fluids, the impervious protective coating is removed and a permeable supporting agent remains to support the individual formation particles. An example of such a supporting agent that is suitable for the process of this invention is waxed paper.

The term propping agent" is used herein to denote any granular solid that is resistant to corrosion and solution by the injected and the formation fluids and has sufficient compressive strength to withstand destruction under the weight of the overburden rock when the injection pressure is decreased and the fracture faces close on the propping agent. The propping agent for example may be composed of glass, plastic, steel, or natural materials such as nut shells, seeds, sand and well rounded pebbles,

having no appreciable abrasive surfaces and having a specific gravity that permits their suspension in the propping liquid. The propping particles should be substantially rounded and are preferably of a size ranging from about four to about forty mesh, US. Standard Sieve Series, to prevent bridging of the propping particles across the entry to the fracture and excessive deposition of propping particles in the well bore. Most materials suitable for use as a propping agent in other formation fracturing processes can be effectively employed in the propping stage of the process of this invention.

The quantity of propping agent required for the effective use of the process of this invention is determined by the necessity of maintaining the fracture open after the release of fluid pressure under the weight of the overburden and the tendency of the unconsolidated formation particles to flow between the individual propping particles. Often a single or double layer of propping agent deposited between the supported fracture faces is effective in maintaining the fracture open and providing a relatively high fluid flow capacity. The term, fluid flow capacity, is defined as the product of the fracture permeability to fluids and the width of the fracture, which is the perpendicular distance between the opposing fracture faces. The fluid flow capacity of a fracture created by the process of this invention is considered adequate if it is at least substantially equal to the flow capacity of the unfractured formation producing throughout its entire depth instead of through the fracture and notched casing. Even in instances where the flow capacity is not greatly increased above that of the unfractured formation, the use of this method is effective in preventing plugging of the well bore by the entry of formation particles into the well and therefore provides a considerable improvement in the production of formation fluids.

When the fracture is allowed to settle under the weight of the overburden rock there is some deformation of the supporting particles around the contiguous propping particles. When this occurs in a fracture propped with only a monolayer or a double layer of propping particles, there can be a significant reduction in the flow capacity of the fracture, Therefore it is preferred that sufficient propping agent be introduced into the fracture to provide at least a substantially complete triple layer of propping particles between the opposing fracture faces.

The carrier liquid for the propping agent can be any liquid that is capable of maintaining the propping agent in suspension during transport and placement of the propping agent, that will not impair significantly the formation or fracture permeability, and that does not corrode or dissolve the supporting agent or the propping agent. The concentration of propping agent in the carrier liquid should be adapted to assure the pumpability of the mixture of propping agent and carrier liquid and to assure that the propping agent will not settle out of suspension in the well bore or bridge the entry of the fracture. To achieve those ends, a concentration of propping agent in the carrier liquid of from about one to about eight pounds of propping agent per gallon of liquid is desirable, and, with the commonly employed carrier liquids such as gelled water and gelled oil, a preferred concentration of propping agent is from about two to about five pounds per gallon of carrier liquid.

The manipulative steps in the application of the process of this invention can be explained more fully with reference to the embodiment presented in the accompanying drawings. In FIGURE 1, an unconsolidated oil-bearing sandstone formation is shown between impervious strata of a cap rock 12 and a base rock 14 penetrated by a well bore 16. A string of well bore casing 18 is set through the unconsolidated formation 10 and secured to the wall of well bore 16 by a sheath of cement 20. A suitable well bore plug 22, such as a retrievable bridge plug, is set in casing 18 below the level of formation 10 to be fractured to isolate the lower portion of the well bore from the portion extending above the depth of the well bore to be fractured.

A circumferential notch 24 is cut through casing 18 and cement sheath 20 into formation 10 by a suitable notching tool. The process of this invention can be used either during the creation and subsequent propping of a fracture in a previously unfractured formation or in the propping of a fracture previously created by other fracturing techniques. FIGURE 1 shows the injection of an aggregate of supporting practicles 26 in a spearhead liquid, not specifically indicated in the drawing, into a fracture 28 around well bore 16. The injection of spearhead liquid into fracture 28 causes supporting particles 26 to be deposited on the fracture faces 30.

After fracture faces 30 have been substantially covered by supporting particles 26 throughout the lateral extent of fracture 28, a carrier liquid, containing propping particles 32, is injected downwardly in well bore 16 through casing 18 into fracture 28 and, as shown in FIGURE 2, the individual propping particles 32 are deposited by the carrier liquid in fracture 28 adjacent the layers of supporting agent 26.

FIGURE 3 shows the condition of well pore 16 and the surrounding formation 10 during the production of fluids from formation 10. The pressure on the liquids in well bore 16 has been released and fracture faces 30 tend to close under the forces exerted by the overbearing rock. A multilayer aggregate of propping agent 32 in fracture 28 maintains faces 30 apart and sustains supporting agent 26 in contact with fracture faces 30 to prevent the movement of individual particles from formation 10 into fracture 28. Generally the compression of propping particles 32 between fracture faces 30 prevents the movement of the propping particles into well bore 16. Although it is not shown in FIGURE 3, it is possible where desirable, to insert in well bore 16 a permeable screen or liner at the level of the fracture. In FIGURE 3, retrievable bridge plug 22 has been removed from well bore 16 but such procedure is optional and depends upon the requirements of a particular well regarding such techniques as simultaneously producing fluids from other formations lower in the well bore. The well completion method described above provides :1 casing cemented through the formation to prevent entry of formation particles into the well bore and a high flow capacity fracture having faces that are permeable to fluids but are supported to prevent movement of formation particles into the fracture.

The effectiveness of this process in providing a high flow capacity propped fracture in an unconsolidated formation is shown by the following tests of the procedure. The Stevens formation of the Paloma Field in California is a poorly consolidated sandstone formation in which conventional fracture propping techniques are ineffective owing to the tendency of the individual formation particles to flow into the interstices between the propping paricles and reduce the fracture permeability to a value approximately equal to that of the formation itself. A core from the Stevens sand, four inches long and three inches in diameter, was molded in epoxy resin and split in half longitudinally. A layer of A inch squares of mesh screen, U.S. Standard Sieve Series, was randomly distributed over the surface of the bottom half of the core to form a substantially complete covering of the exposed sandstone. Then the screens were covered with a three-layer pack of steel balls, each inch in diameter. Another layer of screens was placed on top of the steel propping particles, the upper half of the core was mounted on top of the pack, and the resulting simulated propped fracture was sealed, having only its ends open to flow, to provide an otherwise fluid-tight flow cell.

External loading was then applied over the length of the core to simulate overburden pressure and the fluid flow capacity of the propped fracture in the flow cell was determined. At a simulated overburden pressure of 3000 p.s.i., the how capacity of the fracture was 17,000 millidarcy-feet and, at an overburden pressure of 12,000 psi, the fracture flow capacity was 5000 millidarcy-feet. In a similar test in which a two-layer pack of propping particles was substituted for the three-layer pack of the previous test, the flow capacities at overburden pressure of 3000 p.s.i. and 12,000 p.s.i. were reduced to 2500 and 500 millidarcy-feet, respectively. Thus, the results of the tests show not only the effectiveness of this invention in providing a high flow capacity fracture in a poorly consolidated formation, but also demonstrate the desirability of placing at least a triple layer of propping particles in the fracture to assure a high flow capacity after the fracture faces settle under the force of the overburden pressure.

In anothcr series of tests, a bed of sand was placed in the bottom of a filter press cell and covered with layers of such supporting agents as cloth squares and polyethylene fiakes. Then several layers of propping agent were placed on top of the supporting agent and fluid pressure was applied to the filter press cell. The results of the tests indicated that such supporting agents as cloth and polyethylene flakes are as effective as conventional fluid loss additives in preventing fluid loss during the injection of the fluids and are capable of permitting counterflow through and around the supporting agent during flow of fluids from the formation.

The method of this invention is illustrated further by its application to an unconsolidated sandstone formation at a depth below the surface of from 5180 feet to 5220 feet. A string of V2 inch steel casing is run through the formation and cemented to the wall of the well bore. A notching tool is used to cut a circumferential notch in the casing and formation at a depth of 5200 feet. A retrievable bridge plug is set in the casing below the notch and a packer on a string of 2 /2 inch steel tubing is run in the well. The packer is set approximately ten feet above the notch and the lower end of the tubing is approximately one foot above the notch.

Next a fracture is created around the well bore at the notch by injecting 2000 gallons of spearhead liquid through the tubing and into the notch. The spearhead liquid consists of water to which guar gum has been added to increase the viscosity of the mixture to 30 centipoises. The anticipated fracture radius is approximately 50 feet, providing a combined area of the fracture faces of 15,700 square feet. Sufficient supporting agent is injected to cover four times the area of the fracture faces, i.e. an area of 62,800 square feet. The individual supporting particles are .6 inch squares of oil-insoluble polyvinyl flakes having a thickness of approximately 0.002 inch and a specific gravity of approximately 1.1. To provide the necessary aggregate surface area of the supporting particles requires 145,000,000 particles having a total weight of 710 pounds. Thus the concentration of supporting particles in the spearhead liquid is 72,000 particles per gallon, or approximately 0.35 pound per gallon by weight.

The spearhead liquid is displaced down the tubing and into the fracture by a carrier liquid comprising 2000 gallons of water containing a sufficient concentration of guar gum to provide a mixture having a viscosity of 100 centipoises. The carrier liquid contains eight pounds per gallon of sand. having a grain diameter of from about 0.0331 to about 0.0661 inch, corresponding to 1220 mesh, U.S. Standard Sieve Series. A column of brine is maintained behind the carrier liquid to displace the carrier liquid down the tubing and into the fracture. Pressure on the liquids in the tubing is increased until the formation parts around the notch and the spearhead liquid flows into the fracture, extending it and depositing the polyvinyl flakes on the fracture faces. As the spearhead liquid bleeds into the formation, the carrier liquid flows into the fracture and deposits layers of propping sand between the coated fracture faces. After the fracture is propped, the pressure on the fracturing liquids is reduced, and the fracture faces compress the layers of supporting agent and propping agent together. The ultimate width of the fracture is approximately 0.1 inch and the packing aggregate has a permeability of approximately 300,000 millidarcys, thereby imparting to the fracture a flow capacity of approximately 2500 millidarcy-feet.

The preceding description and examples have been presented merely as an explanation of the concept of the process of this invention and of various possible embodiments thereof. Thus there could occur to one skilled in the art many modifications of this method that are Within the scope and spirit of this invention, such as the use of this process to create a propped fracture having a vertical or other non-horizontal orientation around the well bore. None of the exemplary procedures disclosed herein is intended to limit the scope of this invention which provides a simple, inexpensive and effective method for creating a propped fracture in an unconsolidated rock formation around a cased well bore.

Therefore we claim:

1. A method of propping a fracture in an unconsolidated subterranean rock formation penetrated by a well bore comprising injecting into the fracture a first liquid containing a plurality of lamellar supporting particles, maintaining pressure upon said liquid adapted to hold the lamellae in contact with the faces of the fracture, displacing said first liquid with a second substantially lamellaefree liquid containing a plurality of propping particles, thereafter depositing the propping particles within the fracture with at least some of the propping particles eontiguous to the lamellae, thereby supporting the lamellae in contact with the fracture faces and preventing movement of formation particles into the fracture, and thereafter reducing the pressure on the liquids to leave the lamellae substantially permanently in the fracture adjacent the fracture faces.

2. A method according to claim 1 wherein the lamellae form a substantially continuous covering of the faces of the fracture.

3. A method according to claim 1 wherein the propping particules in the fracture comprise substantially at least a triple layer of propping particles between the fracture faces.

4. A method according to claim 1 wherein each of the lamellae has a longest dimension greater than twice the longest dimension of the individual propping particles.

5. A method according to claim 1 wherein the lamellae comprise pieces of plastic sheeting.

6. A method for propping a fracture in an unconsolidated subterranean rock formation around a well bore penetrating the formation comprising injecting into the well bore a spearhead liquid containing a plurality of lamellar supporting particles, said spearhead liquid having low fluid loss characteristics and a viscosity adapted to maintain the supporting particles in suspension during their transport down the well bore and placement in the fracture, injecting behind the spearhead liquid a substantially lamallae-free carrier liquid containing propping particles and having a viscosity and other fluid properties adapted to maintain the propping particles in suspension during their transport down the well bore and placement in the fracture, displacing the spearhead liquid followed by the carrier liquid into the fracture, maintaining on the liquids pressure adapted to deposit the supporting particles on the fracture faces and to deposit the propping particles within the fracture with at least some of the propping particles contiguous to the supporting particles, and thereafter reducing pressure on the liquids to permit the fracture faces to close on the supporting and the propping particles and thereby leave the lamellae substantially permanently in the fracture adjacent the fracture faces.

7. A method according to claim 6 wherein the carrier e liquid contains propping particles in a concentration of from about one to about eight pounds of propping particles per gallon of carrier liquid.

8. A method according to claim 6 wherein the spearhead liquid contains a quantity of larnellar supporting particles such that the total surface area of the supporting particles available for contact with the fracture faces is equal to at least twice the area of the fracture faces.

9. A method according to claim 6 wherein the spearhead liquid contains a quantity of larnellar supporting particles such that the total surface area of the supporting particles available for contact with the fracture faces is equal to an area of from about four to about ten times the area of the fracture faces.

10. A method for creating a fracture around a well bore penetrating an unconsolidated subterranean rock formation comprising injecting into the well bore a first liquid containing supporting particles having a thickness substantially less than their length and width, injecting behind said first liquid a second substantial supporting particle-free liquid containing granular propping particles, said first liquid positioned in the well bore below the second liquid and adjacent the level of the formation to be fractured, increasing the pressure on said first and second liquids in the well bore until the formation ruptures and a fracture forms therein, maintaining pressure on said first liquid followed by the second liquid to displace the liquids into the fracture away from the well bore, thereby displacing the supporting particles in the first liquid toward the fracture faces and depositing said supporting particles thereon, holding the supporting particles in contact with the fracture faces by maintaining pressure on the liquids, displacing the second liquid into the fracture, thereby depositing the propping particles from the second liquid within the fracture, reducing pressure on the liquids to permit the fracture faces to close and thereafter sustaining substantially permanently the supporting particles against the fracture faces by the propping particles.

11. A method according to claim 10 wherein the supporting particles comprise a plurality of lamellae.

12. A method according to claim 10 wherein the supporting particles comprise a plurality of larnellar particles having a thickness not greater than 0.005 inch, a length of from about inch to about one inch, and a width of from about & inch to about one inch.

13. A method for creating a fracture around a well bore penetrating an unconsolidated subterranean rock formation comprising introducing into the well bore a spearhead liquid containing larnellar supporting particles, increasing pressure on the spearhead liquid until the formation ruptures and a fracture forms therein, introducing a substantially lamellae-free carrier liquid containing granular propping particles into the well bore, thereby displacing the spearhead liquid into the fracture and depositing the supporting particles on the fracture faces, thereafter displacing the carrier liquid into the fracture and depositing the propping particles therein, and thereafter reducing pressure on the liquids to permit the partial closing of the fracture faces and their support by the supporting and the propping particles to leave the supporting particles substantially permanently in the fracture adjacent the fracture faces.

14. A method for fracturing and propping an unconsolidated subterranean rock formation around a well bore penetrating the formation comprising injecting a fracturing liquid into the well here, increasing pressure on the fracturing liquid until the formation ruptures and a fracture forms therein and extends a substantial distance from the well bore, displacing the fracturing liquid down the well bore and into the fracture by injecting into the well bore a spearhead liquid containing larnellar supporting particles, injecting into the well bore a substantially lamellae-free carrier liquid containing granular propping particles, thereby displacing the spearhead liquid into the fracture and depositing the supporting particles on the fracture faces, thereafter injecting the carrier liquid into the fracture and depositing the propping particles therein, and thereafter reducing pressure on the liquids to permit the fracture faces to close on the supporting and the propping particles to leave the supporting particles substantially permanently in the fracture adjacent the fracture faces.

15. A method for completing a well bore penetrating an unconsolidated subterranean rock formation comprising maintaining a column of liquid in the well bore to prevent the entry of formation particles thereinto, running a string of casing into the well bore through the unconsolidated formation, securing the casing in the well bore by depositing a sheath of cement in the annulus between the casing and the wall of the well bore, said cement sheath extending at least through the interval of the unconsolidated formation, creating a circumferential notch through the casing and the cement into the formation at a predetermined level in the well bore, injecting into the well bore and through the notch into the for mation a spearhead liquid containing a plastering agent comprising larnellar particles, injecting behind the spearhead liquid a carrier liquid containing a propping agent comprising granular solid particles, increasing the pressure on the spearhead and carrier liquids to create a fracture in the formation around the notch, maintaining pressure on the liquids adapted to displace the larnellar particles into the fracture in contact with the faces thereof and to displace the granular particles into the fracture with at least some of the granular particles in contact with the larnellar particles, thereafter reducing the pressure on the liquids, thereby permitting the fracture faces to close and preventing entry of the formation particles into the fracture by the restraining force exerted on the fracture faces by the lamellae supported by the granular propping particles.

16. A method of propping a fracture in an unconsolidated subterranean rock formation penetrated by a well bore comprising injecting into the fracture a first liquid containing a plurality of permeable lamellae, each of said lamellae having an impervious outer coating that is soluble in fluids contained in the formation, displacing r said first liquid with a second liquid containing a plurality of solid granules, maintaining a pressure upon said liquids adapted to displace the lamellae into contact with the faces of the fracture and thereafter depositing the granules within the fracture with at least some of the granules contiguous to the lamellae, thereby supporting the lamellae in contact with the fracture faces and preventing the movement of formation particles into the fracture, thereafter reducing the pressure on the liquids and producing the formation fluids through the fracture.

17. A method according to claim 16 wherein the lamellae comprise Wax paper particles.

References Cited by the Examiner UNITED STATES PATENTS 2,562,866 7/1951 Kurtz et al. l6633 X 2,562,867 7/1951 Kurtz et a]. 16633 X 2,650,195 8/1953 Cardwell ct al. l66-33 2,699,212 1/1955 Dismukes l66--42 X 2,788,072 4/1957 Goodwin 16642 X 2,811,207 10/1957 Clark 16642 X 2,950,247 8/1960 McGuire et al. l66-42 X 3,075,581 l/1963 Kern 166-42 3,254,064 5/1966 Nevins -72 X CHARLES E. OCONNELL, Primary Examiner.

JACOB L. NACKENOFF, Examiner.

S. J. NOVOSAD, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 316, 967 May 2, 1967 Jimmie L. Huitt et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 15, after "fracture" insert faces column 3, line 57, after "viscosity" insert range column 4, line 9, for "particles" read particle column 6, line 10, for "practicles" read particles lines 56 and 57, for "paricles" read particles column 9, lines 26 and 27, strike out "first liquid followed by the second liquid to displace the liquids" and insert instead liquids to displacethe first liquid followed by the second liquid Signed and sealed this 21st day of November 1967. (SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A METHOD OF PROPPING A FRACTURE IN AN UNCONSOLIDATED SUBTERRANEAN ROCK FORMATION PENETRATED BY A WELL BORE COMPRISING INJECTING INTO THE FRACTURE A FIRST LIQUID CONTAINING A PLURALITY OF LAMELLAR SUPPORTING PARTICLES, MAINTAINING PRESSURE UPON SAID LIQUID ADAPTED TO HOLD THE LAMELLAE IN CONTACT WITH THE FACES OF THE FRACTURE, DISPLACING SAID FIRST LIQUID WITH A SECOND SUBSTANTIALLY LAMELLAEFREE LIQUID CONTAINING A PLUALITY OF PROPPING PARTICLES, THEREAFTER DEPOSITING THE PROPPING PARTICLES WITHIN THE FRACTURE WITH AT LEAST SOME OF THE PROPPING PARTICLES CONTIGUOUS TO THE LAMELLAE, THEREBY SUPPORTING THE LAMELLAE IN CONTACT WITH THE FRACTURE AND PREVENTING MOVEMENT OF FORMATION PARTICLES INTO THE FRACTURE, AND THEREAFTER REDUCING THE PRESSURE ON THE LIQUIDS TO LEAVE THE LAMELLAE SUBSTANTIALLY PERMANENTLY IN THE FRACTURE ADJACENT THE FRACTURE FACES. 